CAMBRIDGE, England - The papers spent years hidden in a milk churn beneath a Russian dacha and read like an encyclopedia of Cold War espionage.
Original documents from one of the biggest intelligence leaks in history - a who's who of Soviet spying - were released Monday after being held in secret for two decades.
The files smuggled out of Russia in 1992 by senior KGB official Vasili Mitrokhin describe sabotage plots, booby-trapped weapons caches and armies of agents under cover in the West - the real-life inspiration for the fictional Soviet moles in "The Americans" TV series.
In reality, top-quality spies could be hard to get. The papers reveal that some were given Communist honors and pensions by a grateful USSR, but others proved loose-lipped, drunk or unreliable.
Intelligence historian Christopher Andrew said the vast dossier, released by the Churchill Archives Centre at Cambridge University, was considered "the most important single intelligence source ever" by British and American authorities.
Mitrokhin was a senior archivist at the KGB's foreign intelligence headquarters - and a secret dissident. For more than a decade he secretly took files home, copied them in longhand and then typed and collated them into volumes. He hid the papers at his country cottage, or dacha, some stuffed into a milk churn and buried.
After the 1991 collapse of the Soviet Union, Mitrokhin traveled to a Baltic state - which one has never been confirmed - and took a sample of his files to the U.S. Embassy, only to be turned away. So he tried the British embassy, where a junior diplomat sat him down and asked, "Would you like a cup of tea?"
"That was the sentence that changed his life," said Andrew.
Smuggled out of Russia, Mitrokhin spent the rest of his life in Britain under a false name and police protection, dying in 2004 at 81.
The world did not learn of Mitrokhin until Andrew published a book based on his files in 1999. It caused a sensation by exposing the identities of KGB agents including 87-year-old Melita Norwood, the "great-granny spy," who had passed British atomic secrets to the Soviets for years.
Mitrokhin's files describe Norwood as a "loyal, trustworthy, disciplined agent" who was awarded the Order of the Red Banner of Labour for her service.
She was more reliable than the famous "Cambridge Spies," the high-ranking British intelligence officials who worked secretly for the Soviets. The files describe Guy Burgess as "constantly under the influence of alcohol," while Donald Maclean was "not very good at keeping secrets."
The newly released papers include a list of KGB agents in America over several decades. It runs to 40 pages and about 1,000 names.
One of the most notorious was code-named "Dan." He was Robert Lipka, a National Security Agency employee who was paid $27,000 for handing secrets to Russia in the 1960s. After Mitrokhin's information was passed by Britain to U.S. intelligence services, Lipka was arrested and sentenced to 18 years in prison.
The volumes also reveal that Soviet agents stashed weapons and communications equipment in secret locations around NATO countries. Included is a map of Rome showing three caches, along with detailed instructions for finding them. It's unclear how many such weapons dumps have been tracked down by Western authorities.
While some agents targeted the West, many more were deployed inside the Soviet bloc. The files list undercover agents sent to then-Czechoslovakia to infiltrate the dissidents behind the 1968 Prague Spring pro-democracy uprising. Others targeted the entourage of Polish cleric Karol Wojtyla, who would later become Pope John Paul II. The KGB noted with disapproval the future pontiff's "extremely anticommunist views."
The Churchill Archive is giving researchers access to 19 boxes containing thousands of Russian-language files, typed by Mitrokhin from his original handwritten notes. The notes themselves remain classified.
There are glimpses of Mitrokhin's mindset in the titles he gave the volumes, including "The Accursed Regime" and "The Mousetrap."
Andrew said Mitrokhin took huge risks, knowing that "a single bullet in the back of the head" would be his fate if he was caught.
"The material mattered to him so desperately that he was prepared to put his life on the line for it," Andrew said.